1. Field of the Invention
The present invention relates to a revolution controller for a power plant in a cargo-handling vehicle, and more particularly to a revolution controller for controlling a single power plant which is adapted to commonly drive the hydraulic pumps for both driving the vehicle and operating the cargo-handling apparatus.
2. Description of the Prior Art
Heretofore, there have been proposed cargo-handling vehicles equipped with cargo-handling apparatus, such as a forklift truck or shovel loader, etc., in which an engine as a single power plant is used to commonly drive the hydraulic pumps for driving and cargo-handling. A cargo-handling vehicle of this type is so arranged that a pedal is mechanically coupled to a throttle through a wire, link or the like and, when driving the vehicle and when handling cargos, the pedal is stepped on to control the opening position of the throttle, i.e., the speed of the engine, in response to the depressed amount of the pedal.
Accordingly, in driving and cargo-handling, the pedal must be operatively trod in either case, resulting in very troublesome operation. In particular, when operating a cargo-loading apparatus while driving, highly skilled techniques are required.
To solve the above problem, therefore, it can be seen that a cargo-handling device (or cargo-handling operation lever) may be mechanically coupled to the throttle through a wire, link or the like. But such will increase the labor required for operating the cargo-handling device, and lead to many problems in the mechanism and its design, such as the mounting space and arrangement for the link, etc.
In addition, cargo-loading vehicles such as a forklift truck have optimum characteristics at different opening positions of the throttle (or speed of the engine) relative to the depressed amount of the pedal during driving, which are respectively different depending upon various driving conditions such as the presence or absence of cargos, weight of the same, driving on flat or sloped roads, etc.
More specifically, the opening position of the throttle may be varied relative to the depressed amount of the pedal in accordance with, for example, the characteristic of the opening position of the throttle as shown in FIG. 1A when driving on flat roads without cargos, and the characteristic of the opening position of the throttle as shown in FIG. 1B or FIG. 1C when driving on flat roads with cargos, or that as shown in FIG. 1D when taking into account the response of a transmission.
In this connection, because the pedal and the throttle are mechanically coupled to each other as previously mentioned, the characteristics of the opening position of the throttle are uniquely determined relative to the depressed amount of the pedal. As a result, the vehicle cannot be driven while updating the characteristics of the opening position of the throttle to the optimums from time to time depending upon current driving conditions.
Likewise, the pedal is also operated when vertically moving a fork and when longitudinally tilting a mast and, depending upon cargo-handling conditions, there are different optimum characteristics of the opening position of the throttle (or the speed of the engine) relative to the depressed amount of the pedal, for example, as shown in FIGS. 2A-2C when vertically moving the fork, and as shown in FIGS. 3A-3D when longitudinally tilting the mast.
Also in these cases, however, because the pedal and the throttle are mechanically coupled to each other, it is impossible to carry out cargo-handling while updating the characteristics of the opening position of the throttle to optimums from time to time depending upon the current cargo-handling conditions.
Even with the above proposed arrangement including a cargo-handling operating lever mechanically coupled to the throttle, and because the characteristics of the open position of the throttle are uniquely determined relative to the operated amount of the cargo-handling operating lever, it is impossible to carry out cargo-handling while updating the characteristics of the opening position of the throttle relative to the operated amount of the cargo-handling operating lever to different optimums depending upon cargo-handling conditions, as experienced when using the pedal.
Such gives rise to another problem when driving and cargo-handling are to be carried out simultaneously. Stated differently, because of the complicated cross relationships of the foregoing various conditions, conventional mechanical coupling systems do not permit selection of an optimum characteristic of a given engine speed for commonly driving the hydraulic pumps for both driving the vehicle and cargo-handling in one position of the pedal or cargo-handling operating lever.